CAyADIAX FISUEKIEH EXPEDITIOX, Wl-Ho 



119 



It will be seen that the 3'ear-classes 1903 and 1907 were considerably more nume- 

 rously represented in the samples than the other year-classes, and especially charac- 

 teristic is the difference between the " good " year-classes 1907 and 1903, on the ono 

 hand, and the three intermediate years 1904, 1905, and 1906. The older year-classes 

 are represented by few specimens, whereas the younger ones, as mentioned, vary from 

 one sample to another. 



The small number of specimens and of samples, and the nature of the implement 

 of capture, are points which diminish the representative value of the material. On 

 the other hand, the marked degree of similarity between the samples, the characteris- 



1911 10 09 08 07 06 05 04 05 02 01 00 1899 98 97 96 95 



■ 30 % 



- 10 



19U 



218 ind ivid 



1915 



525 Individ. 



1911 10 09 03 07 06 05 04 03 02 01 00 1899 98 97 96 95 



Fig. 30. 



tic transposition of the modes of the curves for 1914-15, and not least, the peculiar 

 course of the curves themselves, are features which must be taken as favouring the 

 supposition that the peculiarities noticeable in the material actually reflect typical 

 conditions. A bimodal or multimodal age curve will probably, as a rule, arise not 

 on account of, but despite the selective effect of the implement of capture. 



We cannot, however, take it for granted that net samples, even though exhibiting 

 variations in the relative strength of the year-classes, present these variations in their 

 correct numerical proportion. If we cannot be sure that the nets have taken the 

 younger year-classes (1911-1910-1909) in their due proportion, neither can we be cer- 

 tain that the two strong year-classes are correctly represented in this respect, the nets 

 might well be supposed to have retained a relatively greater number of the one group 

 than of the other, owing to the difference in size. This question could be decided by 

 continued investigations, or by procuring material from hauls made with non-solect.ive 



